### Please describe the problem.

I need to discover a potentially existing annex-key for any file in the worktree of a Git repository. I assumed that a batch-mode `lookupkey` would be faster than a `find --json --batch`, but that is not the case.

My test repository has 36k files.

```
❯ time git ls-files | git annex lookupkey --batch > /dev/null
git ls-files  0.01s user 0.01s system 0% cpu 2:42.37 total
git annex lookupkey --batch > /dev/null  91.00s user 73.39s system 98% cpu 2:46.25 total

❯ time git ls-files | git annex find --anything --json --batch > /dev/null
git ls-files  0.01s user 0.00s system 0% cpu 4.093 total
git annex find --anything --json --batch > /dev/null  3.20s user 2.02s system 124% cpu 4.195 total
```

`lookupkey` appears to be many times slower than `find`, although the latter reports much more information.

This surprised me, hence I am reporting it here as a potential bug.

### What version of git-annex are you using? On what operating system?

git-annex version: 10.20230126

> [[fixed|done]] --[[Joey]]
